Tire with tread having continuous rib

ABSTRACT

A tyre for a motor vehicle includes a tread and two shoulders. The tread includes a circumferential row of blocks between first and second circumferential grooves. Each of the blocks is delimited by a section of the first circumferential groove and by first and second transverse grooves that terminate at a common vertex spaced from the second circumferential groove. The common vertex is separated from the second circumferential groove by a continuous circumferential tread rib. The second transverse groove delimits one of the blocks and is separated from the first transverse groove that delimits a circumferentially adjacent block by a solid tread portion. The solid tread portion extends from the first circumferential groove to the continuous circumferential tread rib. The common vertex of each block is located at a position axially intermediate the first circumferential groove and a portion of one of the transverse grooves that delimits the block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/318,004, filed Dec. 19, 2008, which is a continuation of U.S.application Ser. No. 10/473,304, filed Sep. 29, 2003, which is anational phase entry under 35 U.S.C. §371 from PCT InternationalApplication No. PCT/EP02/02552, filed Mar. 8, 2002, in the EuropeanPatent Office, the contents of which are relied upon and incorporatedherein by reference. In addition, Applicants claim the benefit ofpriority under 35 U.S.C. §119(a)-(d) based on European PatentApplication No. 01201232.4, filed Mar. 30, 2001, and the benefit ofpriority under 35 U.S.C. §119(e) of U.S. Provisional Application No.60/280,762, filed Apr. 3, 2001. The subject matter of the disclosures ofU.S. application Ser. Nos. 12/318,004, 10/473,304, PCT InternationalApplication No. PCT/EP02/02552, European Patent Application No.01201232.4, and U.S. Provisional Application No. 60/280,762, isincorporated herein by reference.

BACKGROUND

Field of the Disclosure

The present invention relates to a tyre for a motor car. In particular,a high-performance motor car.

Motor vehicle tyres having a tread provided with blocks delimited bycircumferential grooves extending in a substantially longitudinaldirection and by transverse grooves extending in a substantially axialdirection are known. The blocks resulting from the intersection of saidgrooves are formed in various suitably designed shapes and are arrangedin adjacent circumferential rows, each of which is located between twosuccessive circumferential grooves.

The circumferential grooves may influence the directional and travelstability properties of the tyre in relation to the lateral (slip)thrusts directed parallel to the rotation axis of the tyre.

The transverse grooves, in turn, may influence the tractional propertiesof the tyre, namely its capacity to transmit efficiently to the roadsurface the tangential thrusts parallel to the direction of travelduring acceleration and braking of the motor vehicle.

The circumferential and transverse grooves may also influence thedraining of the water in the area making contact with the road surface(footprint area) during travel on a wet road surface.

In any case, the presence of transverse and circumferential groovesinfluences the rolling noise of the tyre. In fact, one of the maincauses of noisiness is the continuous succession of impacts of the edgesof the blocks on the road surface.

A further cause of noisiness consists in dragging of the blocks on theroad surface when they enter and leave the area of contact with the roadsurface. This dragging is due essentially to the deformation of thetread both when the tyre is flattened against the road surface and whenit recovers its inflated condition, as it leaves the area of contactwith the road surface.

The deformations of the tread when coming into contact with and leavingthe area of contact with the road surface also produce a cyclicalvolumetric variation of the grooves which delimit the blocks and aconsequent cyclical action of compression and expansion of the airtrapped inside the grooves. These phenomena of compression and expansionof the air increase the rolling noise of the tyre.

Description of Related Art

Various measures which tend to limit the rolling noise of a tyre areknown. One of these consists in providing the blocks with differentlongitudinal dimensions, by adopting two or more different pitch valuesdistributed in circumferential succession—called “pitch sequence”—suchas to provide the maximum possible lack of uniformity over thecircumferential extension of the tread. The object is to distribute theacoustic energy due to the impacts and dragging of the blocks over awide spectrum of frequencies, thus avoiding concentrating it in aspecific frequency and producing bothersome noise.

The noisiness of a tyre, measured in accordance with the standard ISO/TC31/SC No. 623, is considered unacceptable when it exceeds the followinglimits:

tyre width ≦ 145 72 dB(A) tyre width > 145 and ≦ 165 73 dB(A) tyrewidth > 165 and ≦ 185 74 dB(A) tyre width > 185 and ≦ 215 75 dB(A) tyrewidth > 215 76 dB(A)

The noisiness of tyres is a problem which is difficult to solve becausesome measures which tend to reduce it adversely affect the directional,tractional and water drainage properties.

For example, in order to improve the water drainage properties, thetransverse grooves should be steep, namely they should have a smallinclination with respect to the circumferential grooves. On the otherhand, in order to improve the uniformity of travel and the response timeon a dry road, the transverse channels should have a large inclinationwith respect to the circumferential grooves, namely should besubstantially perpendicular to the longitudinal grooves. However,transverse grooves which are very inclined worsen the rolling noise ofthe tyre.

Moreover, sounds with a frequency of less than 1500 Hz, or moreparticularly less than 1000 Hz, are much more noticeable inside a carthan outside, while sounds with a frequency greater than 1500 Hz aremuch more noticeable outside a car.

Therefore, it is not possible to obtain a low noise level both insideand outside the car and it is difficult to achieve in each case the bestpossible compromise.

EP-812,709 describes a tyre having a tread comprising two regions atleast one of which is provided with a plurality of inclined maingrooves, each of which comprises a segment with a steep inclination anda segment with a slight inclination. A lateral band of the two regionshas an auxiliary groove with a steep inclination communicating with twoadjacent, inclined, main grooves and an auxiliary groove with a slightinclination, situated between the two adjacent, inclined, main grooves.

In a first embodiment, the inclined main grooves extend from acircumferential groove close to the equatorial plane of the tyre, whilein a second embodiment they have a blind bottom.

In a third embodiment, the steeply inclined segments of two adjacent,inclined, main grooves are joined by a thin transverse groove.

EP-867,310 describes a tyre comprising blocks formed in a tread portionby means of a plurality of circumferential grooves and a plurality ofdirectionally inclined grooves. At least some of the directionallyinclined grooves extend from a circumferential groove close to theequatorial plane of the tyre and extend towards one end of the area ofthe tread making contact with the ground. Each of the blocks has anangled portion which forms an acute angle of 10°-60° defined by acircumferential groove and a directionally inclined groove. The surfaceof the angled portion of the block is chamfered over a distance of 10-30mm from a tapered end thereof in a longitudinal direction so as to varygradually towards a portion of larger width.

In the tread of both the abovementioned documents, each inclined groovedelimits a block and the adjacent one located circumferentiallyalongside. Namely, each directionally inclined groove separates twoadjacent consecutive blocks and is common to them.

The result is that both the abovementioned treads have circumferentialrows of sickle-shaped adjacent blocks which are separated only by apitch equal to the sum of the length, in the circumferential direction,of a block and of the adjacent inclined groove.

However, the inventors of the present invention have perceived that thepresence of a considerable number of inclined grooves leading into alongitudinal groove, and their arrangement close to each other,adversely affects the rolling noise of the tyre.

One object of the present invention is a tyre which combines lownoisiness both inside and outside a vehicle, with an excellentperformance on wet and dry road surfaces.

SUMMARY

The present invention relates to a motor car tyre having an equatorialplane and comprising a tread and two shoulders, said tread having atleast one circumferential row of blocks located between a first and asecond circumferential groove, characterized in that each of said blocksis delimited by a section of said first circumferential groove and by afirst and a second transverse groove which extend from said firstcircumferential groove and converge at a common vertex spaced from saidsecond circumferential groove, said common vertex being separated fromsaid second circumferential groove by means of a continuouscircumferential tread rib, said second transverse groove which delimitsa block being separated from a first transverse groove which delimits animmediately following block by a solid tread portion which extends fromsaid first circumferential groove as far as said circumferential rib,forming a single body with said circumferential rib and spacing saidblock and the immediately following block from each other.

Preferably, at least one of said first and second transverse grooves hasan increasing width in the direction from said common vertex towardssaid first circumferential groove.

In one embodiment, at least one of said first and second transversegrooves is sickle-shaped.

Preferably, at least one of said first and second transverse grooves hasa median line formed by an arc of a circle having a predefined radius ofcurvature.

Advantageously, said median line has a first section having a directionsubstantially parallel to said equatorial plane, a second section havinga predefined inclination with respect to said first circumferentialgroove and a linking section which joins together said first and secondsections.

In another embodiment, at least one of said first and second transversegrooves has a first section having a direction substantially parallel tosaid equatorial plane, a second section having a predefined inclinationwith respect to said first circumferential groove and a linking sectionwhich joins together said first and second sections.

Advantageously, each block of said at least one row of blocks is shapedin the form of a shark's fin.

Preferably, the common vertices of said first and second transversegrooves of said at least one row of blocks have the same orientation inthe longitudinal direction.

Typically, said tread has a central circumferential row of blocks and afirst and a second lateral circumferential row of blocks.

In one embodiment, the common vertices of said first and secondtransverse groove of said first lateral row of blocks has an orientationopposite to that of the common vertices of said first and secondtransverse grooves of said central row and second lateral row of blocks.

In another embodiment, the common vertices of said first and secondtransverse grooves of said three rows of blocks have the sameorientation.

Typically, said tread has a first and a second lateral circumferentialrow of blocks and two central circumferential ribs separated by a middlecircumferential groove.

Preferably, the common vertices of said first lateral row of blocks hasan orientation opposite to that of the common vertices of said secondlateral row of blocks.

Advantageously, said first and second transverse grooves of at least oneof said first and second lateral circumferential rows of blocks extendbeyond the respective first circumferential groove and extend into anaxially internal region of one of said shoulders.

Typically, at least one of said shoulders has, in an axially externalregion, pairs of additional transverse grooves converging towards acommon vertex.

Advantageously, said additional converging transverse grooves areseparated from said first circumferential groove by solid portions ofelastomeric material.

Typically, said additional converging transverse grooves extend fromsaid first circumferential groove.

Advantageously, an axially internal region of a shoulder has avoid/solid ratio smaller than that of the axially internal region of theother shoulder and is positioned on the outer side of said motor carwhen said tyre is mounted on said motor car.

The tyre according to the invention ensures a high grip on wet roadsurfaces, very low noise level values both inside and outside the car, ahigh level of comfort and good handling on dry road surfaces.

In particular, in wet road conditions, where the grip is low, the treadaccording to the invention ensures proper drainage of the water withoutaffecting the road holding performance, even at high speeds, both in thelongitudinal direction and in the transverse (lateral) direction. Thisbehaviour is demonstrated by the aquaplaning test around bends, duringwhich the lateral acceleration and the maximum speed which the tyre isable to reach before loss of grip occurs, is measured. When travellingalong a road curvilinear section in very wet conditions, the tyreaccording to the invention maintains for a longer period of time theideal grip conditions with an increase in speed, compared to acomparative tyre.

Moreover, during lateral acceleration, there is a marked improvement inthe maximum acceleration value and the maximum speed value on a wet roadsurface.

Therefore, the tyre according to the invention and the motor car towhich it is fitted have an optimum behaviour in wet road conditions,ensuring greater driving safety.

The high adherence between tyre and wet road surface also ensuresshorter braking distances, thus improving the performance of the motorcar to which the tyre is fitted.

In the present description and the accompanying claims, the term“groove” is understood as meaning a recess having a width not smallerthan 1.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Characteristic features and advantages of the invention will now bedescribed with reference to embodiments illustrated by way ofnon-limiting examples in the accompanying figures in which:

FIG. 1 is a front view of a tyre having a tread provided in accordancewith the invention;

FIG. 2 is a perspective view of the tyre according to FIG. 1;

FIG. 3 is a plan view, on a larger scale, of the tyre tread according toFIG. 1;

FIG. 4 is a plan view of a variant of the tread according to FIG. 3;

FIG. 5 is a plan view of another variant of the tread according to FIG.3;

FIG. 6 is a plan view of a further variant of the tread according toFIG. 3;

FIG. 7 is a plan view of the tread of a comparative tyre;

FIGS. 8-14 are graphs which show the results of tests carried out withthe tyre according to FIG. 1 and with the comparative tyre according toFIG. 7.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 show a tyre 1 with a tread 2 axially delimited by twoshoulders 8 and 12. The tread 2 is provided with circumferential grooves3, 4, 5 and 6 (FIG. 3) which extend in longitudinal direction and areparallel to an equatorial plane 7 of the tyre. The tread 2 includesthree circumferential rows of blocks 9, 10 and 11, a central row 10 andtwo lateral rows 9 and 11. The shoulder 8 is separated from the row ofblocks 9 by means of the circumferential groove 3. The row of blocks 9is located between the circumferential grooves 3 and 4. The row ofblocks 10 is located between the circumferential grooves 4 and 5. Therow of blocks 11 is located between the circumferential grooves 5 and 6.The shoulder 12 is separated from the row of blocks 11 by means of thegroove 6.

The shoulders 8 and 12 comprise an axially internal region 108 and 112,respectively, said axially internal region being closer to theequatorial plane and influencing the performance of the tyre, and anaxially external region 208 and 212, respectively, said axially externalregion being close to one sidewall and not affecting the performance ofthe tyre.

The circumferential grooves 3, 4, 5 and 6 have a width which ranges fromabout 6 mm to about 15 mm and a depth which ranges from about 5 mm toabout 11 mm. In the case of the tread 2 according to FIGS. 1-3, thecircumferential groove 3 has a smaller width, of 9 mm, and depth of 8.2mm, the circumferential grooves 4 and 5 have a greater width, of 13 mm,and depth of 8.8 mm, and the circumferential groove 6 has anintermediate width, of 11 mm, and depth of 8.2 mm.

The row of blocks 9 includes a series of blocks 13, the row of blocks 10includes a series of blocks 14, and the row of blocks 11 includes aseries of blocks 15. The blocks 13, 14 and 15 have the shape of ashark's fin or sickle.

Each block 13 is delimited by a circumferential groove section (base ofthe block) 103 and coupled transverse grooves 16 and 18. The coupledtransverse grooves 16 and 18 extend from ends of the circumferentialgroove section 103 and converge at a common vertex 19, namely meet at acommon point. The common vertex 19 of the coupled grooves 16 and 18 isspaced from the closest circumferential groove 4 by a continuouscircumferential rib 20 of elastomeric material. Each transverse groove18 is separated from each immediately following transverse groove 16 bymeans of a continuous tread portion 21 which extends from thecircumferential groove 3 as far as the circumferential rib 20, forming asingle body with the circumferential rib. Thus the continuous portion oftread 21 separates two immediately consecutive blocks 13. In each row ofblocks the distance between corresponding points of two immediatelyconsecutive blocks 13, measured along the base of the blocks, forms thepitch of the row.

The common vertices 19 of all the coupled transverse grooves 16 and 18have the same orientation in the longitudinal direction. Namely, theblocks 13 of the row 9 have cusps which have the same orientation in thelongitudinal direction.

The transverse grooves 16 and 18 have an increasing width in thedirection from the common vertex 19 towards the circumferential groove3. The groove 16 has a minimum width of 1 mm, a maximum width of 6.1 mmand a depth increasing from 1 mm (vertex 19) to 8.7 mm. The groove 18has a minimum width of 1 mm, a maximum width of 3.2 mm and a depthincreasing from 1 mm (vertex 19) to 8.7 mm.

The grooves 16 and 18 have a curved shape and a respective median line66 and 68 formed by an arc of a circle with a predefined radius ofcurvature. The median line 66 has a section 166 having a directionsubstantially parallel to the equatorial plane 7, a section 266 having apredefined inclination with respect to the circumferential groove 3, anda linking section 366 which joins together the sections 166 and 266.Typically, the radius of curvature of the median line of the grooves 18is 1.5 times the radius of curvature of the median line of the grooves16. In the specific case of the tread 2 (FIG. 3), the radius ofcurvature of the median line 66 of the grooves 16 is 70 mm and theradius of curvature of the median line 68 of the grooves 18 is 105 mm.

Each block 14 is delimited by a circumferential groove section 105 andby respective coupled transverse grooves 26 and 28 having the same shapeas the grooves 16 and 18. The groove 26 has a minimum width of 1 mm, amaximum width of 7.6 mm and a depth increasing from 1 mm (vertex 29) to8.7 mm. The groove 28 has a minimum width of 1 mm, a maximum width of 4mm and depth increasing from 1 mm (vertex 29) to 8.7 mm. The coupledtransverse grooves 26 and 28 converge at a common vertex 29 which isspaced from the closest circumferential groove 4 by a continuouscircumferential rib 24 of elastomeric material. Each transverse groove26 is separated from each immediately following transverse groove 28 bya continuous tread portion 25 which extends from the circumferentialgroove 5 as far as the circumferential rib 24, forming a single bodywith the circumferential rib.

The common vertices 29 of all the coupled transverse grooves 26 and 28have the same orientation in the longitudinal direction and anorientation opposite to that of the common vertices 19 of the coupledtransverse grooves 16 and 18. Namely, the blocks 14 have cusps whichhave an orientation opposite to that of the cusps of the blocks 13.

Each block 15 is delimited by a circumferential groove section 106 andby respective coupled transverse grooves 36 and 38 having the same shapeand the same dimensions as the grooves 26 and 28. The coupled transversegrooves 36 and 38 converge at a common vertex 39 spaced from the closestcircumferential groove 5 by a continuous circumferential rib 30 ofelastomeric material. Each transverse groove 36 is separated from eachimmediately following transverse groove 38 by a continuous tread portion31 which extends from the circumferential groove 6 as far as thecircumferential rib 30, forming a single body with the circumferentialrib.

The common vertices 39 of all the coupled transverse grooves 36 and 38have the same orientation in the longitudinal direction. Theirorientation is the same as that of the common vertices 29 of the coupledtransverse grooves 26 and 28 and opposite to that of the common vertices19 of the coupled transverse grooves 16 and 18.

The pattern of the rows of blocks 10 and 11 is obtained from that of therow of blocks 9 by rotating said row of blocks 9 through 180° about theequatorial plane of the tyre.

The transverse grooves 16 and 18 of the row of blocks 9 have arespective extension 41 and 42 which extends beyond the circumferentialgroove 3 into the axially internal shoulder region 108. The axiallyexternal shoulder region 208 has pairs of transverse grooves 43 and 44which converge at a common vertex 45. The transverse grooves 43 and 44are located between the extensions 41 and 42 and are spaced from thecircumferential groove 3 by means of continuous portions 46 ofelastomeric material.

The transverse grooves 36 and 38 of the row of blocks 11 have arespective extension 51 and 52 which extends beyond the circumferentialgroove 6 into the axially internal shoulder region 112. The axiallyexternal shoulder region 212 has pairs of transverse grooves 53 and 54which extend from the circumferential groove 6 and converge at a commonvertex 55. The transverse grooves 53 and 54 are located in between theextensions 51 and 52.

The common vertices 45 of the pairs of transverse grooves 43 and 44 havethe same orientation in the longitudinal direction. Their orientation isthe same as that of the common vertices 19. The common vertices 55 ofthe pairs of transverse grooves 53 and 54 have the same orientation inthe longitudinal direction. Their orientation is the same as that of thecommon vertices 29 and 39 and opposite to that of the common vertices45.

In the tread 2, the shoulder 8 has a void/solid ratio which is smallerthan that of the shoulder 12. Said shoulder is located on the outer sideof the motor car when the tyre 1 is fitted to the car, whereas theshoulder 12 is located on the inner side.

The tread 2 (FIG. 3) has a void/solid ratio=0.23 in the shoulder 8; avoid/solid ratio=0.23 in the circumferential row of blocks 9; avoid/solid ratio=0.28 in the circumferential row of blocks 10; avoid/solid ratio=0.28 in the circumferential row of blocks 11; and avoid/solid ratio=0.28 in the shoulder 12.

The tread 2 has a pattern of a the asymmetrical type, namely it operatesin a more efficient manner when the tyre is mounted on the motor carwith a given orientation instead of with the opposite one. In otherwords, the tyre preferentially has an inner side (vehicle side) and anouter side. In the tread 2, this is obtained by means of the differentvoid/solid ratio on the two sides: smaller on the outer side and greateron the inner side. The low void/solid ratio on the outer side favoursthe handling of the motor car on a dry road surface, especially if it isa high-performance motor car in which greater camber angles are used,thereby making the footprint of the tyre (tread) asymmetrical.

FIG. 4 shows a tread 62 which is a variant of that shown in FIG. 3 andin which identical parts are indicated by the same numbers. The tread 62is of the asymmetrical directional type, namely has an orientation inthe longitudinal direction which indicates the direction of travel(arrow A). In the tread 62, the common vertices 19, 29 and 39 of thecoupled transverse grooves 16 and 18, 26 and 28, 36 and 38,respectively, have the same orientation in the longitudinal direction.Also the common vertices 45 and 55 have the same orientation of thecommon vertices 19, 29 and 39.

In the tread 62, the shoulder 8 is located on the outer side when thetyre 1 is mounted on the motor car.

FIG. 5 shows a tread 72 which is a variant of that shown in FIG. 3 andin which identical parts are indicated by the same numbers. The patternof the tread 72 is a mirror image of that of the tread 62 and is also ofthe asymmetrical directional type.

FIG. 6 shows a tread 82 which is a variant of that shown in FIG. 3 andin which identical parts are indicated by the same numbers. The tread 82is of the asymmetrical type and includes shoulders 8 and 412, acircumferential row of blocks 209, located between the circumferentialgrooves 3 and 4, a circumferential row of blocks 211, located betweenthe circumferential grooves 5 and 6, and two central circumferentialribs 230 and 231 separated by a middle circumferential groove 232.

The middle circumferential groove 232 has a width which ranges from 1.5to 3 mm and a depth which ranges from 1 to 4 mm. For example, it has awidth of 1.5 mm and a depth of 2 mm.

The row of blocks 209 comprises a series of blocks 213, each of which isdelimited by the circumferential groove section 103 and by two coupledtransverse grooves 216 and 218. The coupled transverse grooves 216 and218 extend from the ends of the circumferential groove section 103 andconverge at a common vertex 219 which is spaced from the closestcircumferential groove 4 by the continuous circumferential rib 20 ofelastomeric material. Each transverse groove 218 is separated from eachimmediately following transverse groove 216 by means of a continuoustread portion 221 which extends from the circumferential groove 3 as faras the circumferential rib 20, forming a single body with thecircumferential rib.

The row of blocks 211 comprises a series of blocks 215, each of which isdelimited by the circumferential groove section 106 and by two coupledtransverse grooves 236 and 238. The coupled transverse grooves 236 and238 extend from the ends of the circumferential groove section 106 andconverge at a common vertex 239 which is spaced from the closestcircumferential groove 5 by the continuous circumferential rib 30 ofelastomeric material.

Each transverse groove 238 is separated from each immediately followingtransverse groove 236 by means of a continuous tread portion 231 whichextends from the circumferential groove 6 as far as the circumferentialrib 30, forming a single body with the circumferential bead.

The coupled transverse grooves 216 and 218, and 236 and 238 comprisesections substantially parallel to the circumferential grooves andsections inclined with respect to the circumferential grooves. Thegrooves 216, 218, 236 and 238 have a width increasing in the directionfrom the vertex 219 or 239 towards the circumferential groove 3 or 6.

The shoulder 412 has, in the axially internal zone 112, extensions 241and 242 of the transverse grooves 236 and 238 and, in the axiallyexternal zone 212, pairs of transverse grooves 243 and 244 whichconverge at a common vertex 245. The transverse grooves 243 and 244 arelocated in between the extensions 241 and 242 and are spaced from thecircumferential groove 6 by means of continuous portions 246 ofelastomeric material.

The pattern of the shoulder 412 is obtained from that of the shoulder 8by rotating said pattern through 180° with respect to the equatorialplane of the tyre.

FIG. 6 indicates by means of an elliptical line F1, the part of thetread pattern which produces a disturbance having a frequencyproportional to the total number of the transverse grooves which undergoan impact in the footprint area. In the area delimited by the ellipticalline F2, the disturbance produced by the pattern is equal to half thetotal number of the abovementioned transverse grooves since they meet inpairs at the same vertex. A further advantage in terms of low noiselevel consists in the fact that said pairs of grooves become blind atthe common vertex of convergence, i.e. they meet in a solid portion ofthe tread and not in an open space such as, for example, an additionalgroove.

The structure of the tyre 1 is per se of the conventional type andcomprises a carcass, a tread band located on the crown of the carcass, apair of axially facing sidewalls terminating in beads reinforced withbead cores and associated bead fillings. The tyre also preferablycomprises a belt structure located between carcass and tread band. Thecarcass is reinforced with one or more carcass plies which are securedto the bead cores, while the belt structure comprises two belt stripswhich are arranged radially on top of each other. The belt strips areformed by portions of rubberised fabric incorporating metal cords whichare parallel to each other in each strip and intersect with those of theadjacent strips, being inclined preferably in a symmetrical manner withrespect to the equatorial plane. Preferably, the belt structure alsocomprises a third belt strip, in a radially outermost position, providedwith cords which are oriented circumferentially, i.e. at zero degreeswith respect to said equatorial plane. The cords of the zero degree beltare preferably made of textiles or even more preferably ofheat-shrinkable material. The tyre 1 has a ratio H/C of the height ofthe right cross-section to the maximum width of the section, rangingbetween 0.65 and 0.20.

Preferably, the tyre 1 is of the type which has a very low cross-sectionwith a ratio H/C of between 0.45 and 0.25.

An example of the tyre according to the invention, having the tread 2according to FIGS. 1-3, was constructed and was subjected to comparativetests with a tyre P shown in FIG. 7.

The comparative tyre P was chosen because it has excellentcharacteristics and has been type-approved for fast and veryhigh-performance sports cars.

The tyre according to the invention had a size of 225/40 R18, with wheelrim of 7.5×18 and inflation pressure of 2.2 bar. The comparative tyrehad the same measurements.

A car, model BMW 328 I, was first equipped with four tyres according tothe invention and then with four comparative tyres.

Aquaplaning tests were carried out along straight road sections andaround bends, together with braking tests on dry and wet road surfaces,handling tests on dry and wet road surfaces, tests for noise inside andoutside the car, and comfort tests.

The aquaplaning test along the straight was carried out along a straightsection of smooth asphalt, of predefined length (100 m), with a layer ofwater of predefined constant height (7 mm) which was automaticallyrestored after each test vehicle had passed by. The vehicle entered at aconstant speed (approximately 70 km/h) in conditions of perfect grip andaccelerated until the conditions of total loss of grip occurred.

The aquaplaning test around bends was carried out along a road sectionwith smooth and dry asphalt, around a bend with a constant radius (100m), having a predefined length and comprising, along a final section, azone of predefined length (20 m) flooded with a layer of water ofpredefined thickness (6 mm). The test was carried out at a constantspeed for different speed values.

During the course of the test, the maximum centrifugal acceleration andthe maximum speed of the car corresponding to complete aquaplaning wererecorded.

The braking test was carried out along a straight section of asphaltboth in dry and wet conditions, recording the stopping distance from apredefined initial speed, typically 100 km/h in dry conditions and 80km/h in wet conditions. The stopping distance is determined as themathematical average of a series of successive recorded values.

The handling test, in dry and wet surface conditions, was carried outalong predefined sections, typically of circuits closed to traffic. Bymeans of the simulation of certain characteristic manoeuvres (such aschange of lane, overtaking, slalom between skittles, entering andleaving a bend) carried out at constant speed, as well as duringacceleration and deceleration, the performance of the tyre was assessedby the test driver by assigning a numerical evaluation for the tyrebehaviour during the abovementioned manoeuvres.

The evaluation scale represents a subjective opinion expressed by thetest driver during tests carried out in sequence on the equipment beingcompared.

The noise tests were carried out both indoors and outdoors.

The indoor tests were carried out in an externally sound-proofed chamber(semianechoic chamber) by using the abovementioned motor car equippedfirst with a tyre according to the invention and then with a comparativetyre, keeping the tyre in contact with a rotating drum made to rotate atdifferent speeds. Microphones were arranged inside and outside the carin order to measure, respectively, the internal noise and externalnoise.

The outdoor test was carried out along a straight section equipped withmicrophones. The car entered the section at a predefined speed of entry,after which the engine was switched off and the noise outside the car inneutral gear was measured.

The comfort was evaluated in terms of the overall sensations perceivedby the test driver compared to the capacity for the tyre to absorb theroughness of the road surface.

The noise and comfort tests were carried out in the conditionsprescribed by the standard RE01.

The results of the tests are shown in Table I where the values assignedare expressed as a percentage against the values of the comparative tyrefixed at 100.

TABLE I Tyre according to Comparative tyre the invention Aquaplaningalong straight 100 105 sections Aquaplaning around bends 100 110 Brakingon dry surface 100 103 Braking on wet surface 100 107 Handling on drysurface 100 100 Handling on wet surface 100 105 Internal noise 100 100External noise* 100 110 Comfort 100 100 *Values recorded during outdoortests

In Table I, the values greater than 100 indicate an improvement withrespect to the comparative tyre.

The results of the tests show that the tyre according to the inventionhas a behaviour which is markedly better than that of the comparativetyre in the tests carried out for braking on wet surfaces and externalnoise.

FIGS. 8 and 9 show the graphs relating to the noise level in dB(A)outside (FIG. 8) and inside (FIG. 9) the car in relation to the speed(km/h) ranging from 150 to 20 km/h. The graphs A and A1 relate to thecomparative tyre, while the graphs B and B1 relate to the tyre accordingto the invention. It may be noted that the tyre according to theinvention has an external noise level which is lower than that of thecomparative tyre by on average 1.5 dB(A), while the internal noise levelis substantially equivalent to that of the comparative tyre.

FIGS. 10, 11, 12 and 13 are three-dimensional graphs which show theprogression of the sound pressure (Pa) of the phonometric signal inrelation to the speed (km/h) and the frequency (Hz).

FIG. 10 refers to the internal noise of the motor car equipped with thecomparative tyres. FIG. 12 refers to the noise inside the motor vehicleequipped with the comparative tyres.

As can be seen from the graphs, the tyre according to the invention hasa noise distribution in three different frequency ranges: the lowfrequency range (0-300 Hz), the range of frequencies characteristic ofthe pitch of the tyre (800-1600 Hz) and a further middle frequency range(300-800 Hz).

The comparative tyre, although producing on average a low-intensitynoise level, concentrates all the disturbance in the low and highfrequencies.

The tyre according to the invention, on the contrary, by distributingmore uniformly the noise over the whole frequency range, produces anoise which is perceived in a more attenuated manner.

FIG. 11 refers to the noise outside the motor car equipped with thetyres according to the invention. FIG. 13 refers to the noise outsidethe car equipped with the tyres according to the invention.

Unlike the graphs relating to the internal noise, those relating to theexternal noise do not have the low-frequency range characteristic of thetransmission of the noise “via solid” (through the car). On the otherhand, the noise generated in the medium and high frequency range whichextends up to 2500 Hz (transmission “via air”) is emphasized. The tyreaccording to the invention also produces in this case a distribution ofthe noise over a wider frequency band, attenuating the average intensitythereof.

FIG. 14 shows the graphs for the intensity of the external noise dB(A)in relation to the speed (km/h) for the tyre according to the invention(graph B2) and for the comparative tyre (graph A2).

The graphs show the result of so-called “coast-by-noise” tests (ISO362-1981, Amendment 1, published 1985) carried out with the motor cardescribed above on the track of Vizzola Ticino in accordance with thestandard ISO 10844. As is known, during these tests the reference speedis 80 km/h.

The graphs according to FIG. 14 show that the tyre according to theinvention has proved to be less noisy than the comparative tyre by 2dB(A).

The invention claimed is:
 1. A tyre for a motor vehicle, comprising: atread; and two shoulders; wherein the tread comprises a circumferentialrow of blocks disposed between first and second circumferential grooves,wherein each of the blocks is delimited by a section of the firstcircumferential groove and by first and second transverse grooves thatterminate at a common vertex spaced from the second circumferentialgroove, wherein the first and second transverse grooves of thecircumferential row of blocks are oriented in a first direction along alongitudinal direction of the tread, wherein the common vertex isseparated from the second circumferential groove by a continuouscircumferential tread rib, wherein the second transverse groove delimitsa first one of the blocks and is separated from the first transversegroove that delimits a circumferentially adjacent block by a solid treadportion, wherein at least one of the first and second transverse groovescomprises an increasing width in a direction from the common vertextoward the first circumferential groove, wherein the solid tread portionextends from the first circumferential groove to the continuouscircumferential tread rib, wherein the solid tread portion forms asingle body with the continuous circumferential tread rib, spacing thefirst block and the circumferentially adjacent block from each other,and wherein the common vertex of each block is located at a positionaxially intermediate the first circumferential groove and a portion ofone of the transverse grooves that delimits the block.
 2. The tyre ofclaim 1, wherein at least one of the first and second transverse groovesfurther comprises: a first section comprising a direction substantiallyparallel to an equatorial plane of the tyre; a second section comprisinga predefined inclination with respect to the first circumferentialgroove; and a linking section joining together the first and secondsections.
 3. The tyre of claim 1, wherein at least one of the first andsecond transverse grooves is sickle-shaped.
 4. The tyre of claim 1,wherein at least one of the first and second transverse groovescomprises a median line formed by an arc of a circle comprising apredefined radius of curvature.
 5. The tyre of claim 4, wherein themedian line comprises: a first section comprising a directionsubstantially parallel to an equatorial plane of the tyre; a secondsection comprising a predefined inclination with respect to the firstcircumferential groove; and a linking section joining together the firstand second sections.
 6. The tyre of claim 1, wherein the first andsecond transverse grooves of the circumferential row of blocks extendbeyond the first circumferential groove and into an axially internalregion of one of the shoulders.
 7. The tyre of claim 1, wherein eachblock of the circumferential row of blocks is shaped in a form of ashark's fin.
 8. The tyre of claim 1, wherein the circumferential row ofblocks is a first central circumferential row of blocks, the treadfurther comprising first and second lateral circumferential rows ofblocks.
 9. The tyre of claim 8, wherein each of the blocks of the firstand second lateral circumferential rows of blocks is delimited by firstand second transverse grooves, and wherein the first and secondtransverse grooves of the first and second lateral circumferential rowsof blocks extend beyond a circumferential groove and into an axiallyinternal region of one of the shoulders.
 10. The tyre of claim 1,wherein the circumferential row of blocks is a first centralcircumferential row of blocks, the tread further comprising: a secondcentral circumferential row of blocks disposed between third and fourthcircumferential grooves; and first and second central circumferentialribs, wherein the first central circumferential rib is separated fromthe first central circumferential row of blocks by the secondcircumferential groove, wherein the first central circumferential rib isseparated from the second central circumferential rib by a middlecircumferential groove, and wherein the second central circumferentialrib is separated from the second central circumferential row of blocksby the third circumferential groove.
 11. The tyre of claim 10, whereinthe continuous circumferential tread rib is a first continuouscircumferential tread rib and the common vertex is a first commonvertex, wherein second common vertices of the second centralcircumferential row of blocks have an orientation, wherein each of theblocks is delimited by a section of the fourth circumferential grooveand by first and second transverse grooves that extend from the fourthcircumferential groove and terminate at a second common vertex spacedfrom the third circumferential groove, wherein the first and secondtransverse grooves of the second central circumferential row of blocksare oriented in the opposite direction of said first direction along thelongitudinal direction of the tread, and wherein the second commonvertex is separated from the third circumferential groove by a secondcontinuous circumferential tread rib.
 12. The tyre of claim 10, whereinthe first and second transverse grooves of at least one of the first andsecond central circumferential rows of blocks extend beyond a respectivefirst or fourth circumferential groove and into an axially internalregion of one of the shoulders.
 13. The tyre of claim 1, wherein thecommon vertex is a first common vertex, and wherein at least one of theshoulders comprises, in an axially external region, pairs of additionaltransverse grooves converging toward a second common vertex.
 14. Thetyre of claim 13, wherein the additional transverse grooves areseparated from the first circumferential groove by solid portions ofelastomeric material.
 15. The tyre of claim 14, wherein an axiallyinternal region of a first shoulder comprises a void/solid ratio smallerthan that of an axially internal region of a second shoulder, andwherein the first shoulder is positioned on an outer side of the motorvehicle when the tyre is mounted on the motor vehicle.
 16. The tyre ofclaim 13, wherein the additional transverse grooves extend from thefirst circumferential groove.
 17. The tyre of claim 16, wherein anaxially internal region of a first shoulder comprises a void/solid ratiosmaller than that of an axially internal region of a second shoulder,and wherein the first shoulder is positioned on an outer side of themotor vehicle when the tyre is mounted on the motor vehicle.
 18. Thetyre of claim 1, wherein the tyre defines an equatorial plane, and thecircumferential row of blocks is disposed co-extensive with theequatorial plane.
 19. A tyre for a motor vehicle, comprising: a tread;and two shoulders; wherein the tread comprises a circumferential row ofblocks disposed between first and second circumferential grooves,wherein each of the blocks is delimited by a section of the firstcircumferential groove and by first and second transverse grooves thatterminate at a common vertex spaced from the second circumferentialgroove, wherein the first and second transverse grooves of thecircumferential row of blocks are oriented in a first direction along alongitudinal direction of the tread, wherein the common vertex isseparated from the second circumferential groove by a continuouscircumferential tread rib, wherein the second transverse groove delimitsa first one of the blocks and is separated from the first transversegroove that delimits a circumferentially adjacent block by a solid treadportion, wherein the solid tread portion extends from the firstcircumferential groove to the continuous circumferential tread rib,wherein the solid tread portion forms a single body with the continuouscircumferential tread rib, spacing the first block and thecircumferentially adjacent block from each other, wherein the tyredefines an equatorial plane, and the circumferential row of blocks isdisposed co-extensive with the equatorial plane, and wherein the commonvertex of each block is located at a position axially intermediate thefirst circumferential groove and a portion of one of the transversegrooves that delimits the block.
 20. The tyre of claim 19, wherein atleast one of the first and second transverse grooves further comprises:a first section comprising a direction substantially parallel to anequatorial plane of the tyre; a second section comprising a predefinedinclination with respect to the first circumferential groove; and alinking section joining together the first and second sections.
 21. Thetyre of claim 19, wherein at least one of the first and secondtransverse grooves is sickle-shaped.
 22. The tyre of claim 19, whereinat least one of the first and second transverse grooves comprises amedian line formed by an arc of a circle comprising a predefined radiusof curvature.
 23. The tyre of claim 22, wherein the median linecomprises: a first section comprising a direction substantially parallelto an equatorial plane of the tyre; a second section comprising apredefined inclination with respect to the first circumferential groove;and a linking section joining together the first and second sections.24. The tyre of claim 19, wherein each block of the circumferential rowof blocks is shaped in a form of a shark's fin.
 25. The tyre of claim19, wherein the circumferential row of blocks is a first centralcircumferential row of blocks, the tread further comprising: first andsecond lateral circumferential rows of blocks.
 26. The tyre of claim 25,wherein each of the blocks of the first and second lateralcircumferential rows of blocks is delimited by first and secondtransverse grooves, and wherein the first and second transverse groovesof the first and second lateral circumferential rows of blocks extendbeyond a circumferential groove and into an axially internal region ofone of the shoulders.
 27. The tyre of claim 19, wherein the commonvertex is a first common vertex, and wherein at least one of theshoulders comprises, in an axially external region, pairs of additionaltransverse grooves converging toward a second common vertex.
 28. Thetyre of claim 27, wherein the additional transverse grooves areseparated from the first circumferential groove at least by solidportions of elastomeric material.
 29. The tyre of claim 28, wherein anaxially internal region of a first shoulder comprises a void/solid ratiosmaller than that of an axially internal region of a second shoulder,and wherein the first shoulder is positioned on an outer side of themotor vehicle when the tyre is mounted on the motor vehicle.
 30. Thetyre of claim 27, wherein an axially internal region of a first shouldercomprises a void/solid ratio smaller than that of an axially internalregion of a second shoulder, and wherein the first shoulder ispositioned on an outer side of the motor vehicle when the tyre ismounted on the motor vehicle.
 31. The tyre of claim 19, wherein at leastone of the first and second transverse grooves comprises an increasingwidth in a direction from the common vertex toward the firstcircumferential groove.
 32. A tyre for a motor vehicle, comprising: atread; and two shoulders; wherein the tread comprises a circumferentialrow of blocks disposed between first and second circumferential grooves,wherein each of the blocks is delimited by a section of the firstcircumferential groove and by first and second transverse grooves thatterminate at a common vertex spaced from the second circumferentialgroove, wherein the first and second transverse grooves of thecircumferential row of blocks are oriented in a first direction along alongitudinal direction of the tread, wherein the common vertex isseparated from the second circumferential groove by a continuouscircumferential tread rib, wherein the second transverse groove delimitsa first one of the blocks and is separated from the first transversegroove that delimits a circumferentially adjacent block by a solid treadportion, wherein the solid tread portion extends from the firstcircumferential groove to the continuous circumferential tread rib,wherein the solid tread portion forms a single body with the continuouscircumferential tread rib, spacing the first block and thecircumferentially adjacent block from each other, and wherein the commonvertex of each block is located at a position axially intermediate thefirst circumferential groove and a portion of one of the transversegrooves that delimits the block.
 33. The tyre of claim 32, wherein atleast one of the first and second transverse grooves further comprises:a first section comprising a direction substantially parallel to anequatorial plane of the tyre; a second section comprising a predefinedinclination with respect to the first circumferential groove; and alinking section joining together the first and second sections.
 34. Thetyre of claim 32, wherein at least one of the first and secondtransverse grooves is sickle-shaped.
 35. The tyre of claim 32, whereinat least one of the first and second transverse grooves comprises amedian line formed by an arc of a circle comprising a predefined radiusof curvature.
 36. The tyre of claim 35, wherein the median linecomprises: a first section comprising a direction substantially parallelto an equatorial plane of the tyre; a second section comprising apredefined inclination with respect to the first circumferential groove;and a linking section joining together the first and second sections.37. The tyre of claim 32, wherein the first and second transversegrooves of the at least one row of blocks extend beyond the firstcircumferential groove and into an axially internal region of one of theshoulders.
 38. The tyre of claim 32, wherein each block of thecircumferential row of blocks is shaped in a form of a shark's fin. 39.The tyre of claim 32, wherein the circumferential row of blocks is afirst central circumferential row of blocks, the tread furthercomprising: first and second lateral circumferential rows of blocks. 40.The tyre of claim 39, wherein each of the blocks of the first and secondlateral circumferential rows of blocks is delimited by first and secondtransverse grooves, and wherein the first and second transverse groovesof the first and second lateral circumferential rows of blocks extendbeyond a circumferential groove and into an axially internal region ofone of the shoulders.
 41. The tyre of claim 32, wherein thecircumferential row of blocks is a first central circumferential row ofblocks, the tread further comprising: a second central circumferentialrow of blocks disposed between third and fourth circumferential grooves;and first and second central circumferential ribs, wherein the firstcentral circumferential rib is separated from the first centralcircumferential row of blocks by the second circumferential groove,wherein the first central circumferential rib is separated from thesecond central circumferential rib by a middle circumferential groove,and wherein the second central circumferential rib is separated from thesecond central circumferential row of blocks by the thirdcircumferential groove.
 42. The tyre of claim 41, wherein the continuouscircumferential tread rib is a first continuous circumferential treadrib and the common vertex is a first common vertex, wherein secondcommon vertices of the second central circumferential row of blocks havean orientation, wherein each of the blocks is delimited by a section ofthe fourth circumferential groove and by first and second transversegrooves that extend from the fourth circumferential groove and terminateat a second common vertex spaced from the third circumferential groove,wherein the first and second transverse grooves of the second centralcircumferential row of blocks are oriented in the opposite direction ofsaid first direction along the longitudinal direction of the tread, andwherein the second common vertex is separated from the thirdcircumferential groove by a second continuous circumferential tread rib.43. The tyre of claim 41, wherein the first and second transversegrooves of at least one of the first and second central circumferentialrows of blocks extend beyond a respective first or fourthcircumferential groove and into an axially internal region of one of theshoulders.
 44. The tyre of claim 32, wherein the common vertex is afirst common vertex, and wherein at least one of the shoulderscomprises, in an axially external region, pairs of additional transversegrooves converging toward a second common vertex.
 45. The tyre of claim44, wherein the additional transverse grooves are separated from thefirst circumferential groove by solid portions of elastomeric material.46. The tyre of claim 45, wherein an axially internal region of a firstshoulder comprises a void/solid ratio smaller than that of an axiallyinternal region of a second shoulder, and wherein the first shoulder ispositioned on an outer side of the motor vehicle when the tyre ismounted on the motor vehicle.
 47. The tyre of claim 44, wherein theadditional transverse grooves extend from the first circumferentialgroove.
 48. The tyre of claim 47, wherein an axially internal region ofa first shoulder comprises a void/solid ratio smaller than that of anaxially internal region of a second shoulder, and wherein the firstshoulder is positioned on an outer side of the motor vehicle when thetyre is mounted on the motor vehicle.
 49. The tyre of claim 32, whereinat least one of the first and second transverse grooves comprises anincreasing width in a direction from the common vertex toward the firstcircumferential groove.
 50. The tyre of claim 32, wherein the tyredefines an equatorial plane, and the circumferential row of blocks isdisposed co-extensive with the equatorial plane.